Summarize local phone storage in MemoryStatusActivity.

As the first item in the list, find the number of Contacts stored on the
device with PhoneAccountType.ACCOUNT_TYPE.

Depends on http://review.cyanogenmod.org/#/c/91855/ to display
correctly.

Change-Id: Ib421a1e9e2fa99310f5591c8db75c9a48b93b3ee
(cherry picked from commit 01b69c2b)